Smoke Control

[907DAVE]

Here is an interesting post Charles made on the Nation a while back.

Can you go too lean? As much as we all got a kick out of poking fun at the wizzer on his glorious "lean out" run....

Over the past year or so I have noticed something, and I've made reference to it a few times before. If you pull fuel, you MUST pull timing/icp all else constant. It goes WITHOUT FAIL in my truck, that a simple drop of say 1ms of pw, will result in utter violence from the engine, and the sound of advanced timing. At one point recently I was down to 0 degrees of timing, and 2200psi at WOT just to try and stop it. Couldn't be done. The engine was NEVER happy like that. Running clean as a whistle, and making probably mid 500's, but very, very noticeably less happy.

Back when I was running Jonathan's stuff without alteration on my own, I always noticed that the "hot" file would ALWAYS be much, much smoother than the midrange program. Just smooth as silk in the full on program leaving smoke as far as the eye could see, and rough and ragged in the midrange program running clean as a whistle, and making 50 or so less hp. Working with him on those files a bit, I know for a fact that the ICP/Timing was the same on them.

That taught me two things....

First, more fuel will "soften" an engine out once you crest the smoke limit.

Secondly, less fuel down low will light the FUK out of a charger. As was the case, where my midrange program would blow the tires off just nailing the throttle at times, and zip right up, while the "hot" program would smolder, and smolder and finally light off. Smooth, but sluggish.


Those are basic facts of life with a diesel IMO. Too much fuel at spoolup.... and you get bad sluggish response. Too little fuel after spoolup, and you get ragged, unhappy performance.... that I have NO doubt would kill and engine in short order if left unchecked.



So............. why?

Well, since I can't crawl inside the cylinder and see for myself. All I can do is hypothesize (figured I demonstrate correct usage )

IMO, the spoolup issue is simple. You inject too much fuel and you put the fire out, and get smoldering sh*t going down the line to try and light the charger. Rpm won't come up, power won't come up, and you've got nothing to spin up the charger but cold smoke. That one's easy....

As to needing more fuel up top at full power...

Here's what I've gathered to date. If you think about the likely scenario playing out in the cylinder, you have fuel being injected, heating, begining to burn, and once the burn commences, it can easily burn rather quickly if the stage is set appropriately. Far TOO quickly if you don't watch your ***.

If you just shoot a tiny little spurt of fuel in the cylinder, it will start to burn, and then flash off rather quickly without much issue. No real pressure to speak of, and no real power either because the BMEP will be very low considering the limited crank angle through which it exerted good cylinder pressure. Okay fine. We'll call this a mild program.

So what if you inject say, twice that much fuel now. Well, now you've got the same flashing off, except there is twice as much fuel once it starts to flash, and the injector has also turned off about this time, so there's no more cold fuel (relative to the cylinder temp) being injected that needs a moment to heat before combusting. So? BAM! It all just pops, and flashes off reeeeal quick. When I get in this range with my truck, I call it "crispy". You have to REALLY watch your *** here. A bit too much of ANYTHING and you can create some scary cylinder pressures with modest fuel quantities, and as I said, insanely LOW timing/ICP values. Obviously pulling enough timing would stop it, but now you're pissing away power, and creating heat with this all flashing off late.

So? Add twice again more fuel...... And it STOPS!

That's right. Dowse it down with fuel, and the "extra crispy" bs stops. Immediately, WITHOUT FAIL.

I personally believe this to be due to the fact that you have a constant flow of incoming fuel that will not ever allow the fuel to "flash" off and "round the corner" where it's still in the meat of the cylinder temperature/pressure (near TDC) when you cut the injector off. If you turn the injector off while it's still flashing hard the fuel pocket just EXPLODES, and tried to send your heads into the hood. You can feel it if you've played with timing and cylinder pressure a bit. It is not good.

Trying to pull fuel has proven to be IMPOSSIBLE for me. The only way to calm the truck is to pull boost. That allows me to alter the burn RATE, not the quantity/time. And as such, I'm not really sure how to make good power, without smoking and not be putting extra stress on the engine.

I'm going back to laying fuel down on the ground at WOT and using water to control the EGT.

We'll see.


But I ABSOLUTELY believe that too little fuel/ too much air can and will cause very substantial problems for a diesel engine in certain scenarios.

I see it everyday. If you start burning every drop of fuel, you better make sure you've got the tune SPOT-ON, or I expect you would hurt things in a hurry.

And mattr66's version

what happens to a cutting torch when you go from the proper flame and start taking away the acetelene while leaving the oxygen flow the same.........POP!

Very interesting stuff..........but is defiantly throws a stick in my spokes.

[cleatus12r]

Dave,

I have personally experienced this on many occasions and I really began to notice it on a stock fueled truck with a slightly "smoothed" base SOI map. Dropping ICP in the "advanced" regions quieted it down.

To be completely honest with you, I was actually looking for that exact post a few days ago.

[907DAVE]

Well I have been working on making my Daily program smoke free. It was pretty good but I was experiencing excessive smoke on a 50-60 mph "roll on". I was able to get it juuust about completely smoke free by dropping PW in this certain area of the map..........

Problem now is at lower speeds, parking lots, driveways, etc the truck will slowly pick up speed and then launch forward without changing the APP. Basically when I am trying to maintain a slow speed the truck will accelerate quickly without me asking it to. Prior to making these adjustment the truck behaved PERFECT, besides the smoke.

Another issue I created is a 150 RPM rolling idle.

Here is what the map looks like.........



I tried adjusting the ICP map to lessen the "ramp up" with seemingly no change.

My only guess now is I am having an ICP issue, maybe compensating for such low PW.

Did I go too far with the PW map?

Should I be making my adjustments somewhere else?

Be easy on me......I am new.

[thedieselguru]

Dave,

As I understand it, part of the issue is timing. The other part is to atomize the fuel. In that, if you advance timing then you can burn fuel that isn't "broken up" as well. But if you retard timing, you have to really atomize the fuel for complete burn.

The example being HPCR systems. The closer to TDC you SOI, the higher the rail pressure and vise versa. In a HEUI, the ICP and intensifier piston accomplishes what rail pressure does in those systems. Controls injection pressure at the nozzle.

All that being said, I would think that a lower ICP and a little advance in SOI would make less smoke without the "lean burn" feel. With a bump in PW to keep the fuel delivery the same.

But I might be way off base???

Roger

[907DAVE]

Well my issue is that I am running injectors that are roughly 3 times as big as stock injectors, and can deliver this fuel in about half the time. Because of the faster delivery rate I do not want to add any more timing to reduce smoke. The other part of the problem lies in the injector nozzles being so large, I loose atomization, and the only way to get this back is to increase ICP. I am not sure how to add any more ICP without any negative side affects, like I am experiencing now.

[907DAVE]

Damn it.........I think I finally realized what I did wrong.

If I quit thinking about it then all of a sudden it pops into my head.

[cleatus12r]

Originally Posted by 907dave

Damn it.........I think I finally realized what I did wrong.

If I quit thinking about it then all of a sudden it pops into my head.

It's funny you mentioned that. I was going to give you a "pop quiz" based on the questions you asked in the previous post.

ALL RIGHT!!!

[thedieselguru]

Well don't keep us in suspence, man?